The object of this invention is to reduce or prevent the fading of dyed nylon fabrics caused by ozone. By fading is meant loss of fastness of the dye, i.e., the dye becomes less bright or changes color, for example, dark blue to light blue.
Ozone is present in air at sea level at a concentration of only 1 to 5 parts per hundred million. Only under conditions of heavy smog does it rise as high as 60 parts per hundred million. Despite this extremely low concentration of ozone, severe fading is observed.
Ozone is an allotropic form of oxygen. The molecule of ozone consists of three atoms of oxygen whereas a molecular of oxygen contains two atoms of oxygen. Ozone is formed in the upper atmosphere by the action of high energy radiation from the sun splitting oxygen molecules into two oxygen atoms. These atoms then combine with oxygen (O.sub.2) molecules to form ozone (O.sub.3). This ozone then diffuses down through the atmosphere.
Ozone is an electrophilic reagent, that is, it searches out and attacks electron pairs such as those existing with carbon-carbon double bonds.
The dyes which are attacked are usually anthraquinone type disperse dyes, although it is believed that under severe conditions almost all dyes might be affected by ozone. Cationic dyes are also susceptible.
One of the most sensitive dyes to ozone fading is Disperse Blue 3. The major constituent of Disperse Blue 3 has the structure: ##SPC1##
Basic anthraquinone dyes, such as C. I. Basic Blue 47, are also subject to ozone fading as shown in Examples II to IV. Typical anthraquinone dyes are shown by U.S. Pat. No. 2,900,216. Analysis of C. I. Basic Blue 47 or Astrazon Blue 3RL has shown it is quaternized from the compound labeled 2 in the list of compounds on page 1 of U.S. Pat. No. 2,900,216. Thus, the structure would be: ##SPC2##
Where A is an anion, such as Cl.sup.-. The 1963 Supplement of the Colour Index also indicates Astrazon Blue 3RL is an anthraquinone.
The dye diffuses through the fiber to contact the ozone at the surface of the fiber. Part of the evidence for this is that any treatment or additive that increases the mobility of the dye, increases its ozone fading.
There is some evidence that water is necessary to give ozone fading, but whether its action is that it swells the nylon or is involved in a primary or secondary oxidation step is unclear.
Ozone fading can be decreased by reduction of the specific surface area of the yarn. This is undesirable when a bulky yarn is required. Ozone fading can also be decreased by changes in polymer morphology and orientation but these techniques are inherently expensive.